This present invention relates to a method for introgressing a form of seedlessness, viz. stenospermocarpy (SSC) from subgenus Euvitis Planch. into subgenus Muscadinia Planch. and the plants produced by the method. All publications cited in this application are herein incorporated by reference.
The goal of plant breeding is to combine in a single variety or hybrid various desirable traits. For fruiting crops, such as grapes (Vitis), these traits may include resistance to diseases and insects, tolerance to heat and cold, greater yield, better viticultural quality, high concentrations of anti-oxidant phytochemicals, ease of hand or mechanical harvesting of berries, uniform berry size and color, and pleasant aroma and flavor.
Grapes botanically belong to the family Vitaceae, which is divided into 16 genera. Of these, Vitis is the only genus with economic importance. The genus Vitis is divided into two subgenera, Euvitis Planch. and Muscadinia Planch. The subgenus Euvitis has 38 chromosomes and many berries borne in each cluster so that the general term ‘bunch grape’ is given to all species of Euvitis. Muscadinia has 40 chromosomes and smaller clusters, with a common name of muscadine grape.
More than 60 species have been described in Euvitis, including hundreds of known cultivars, which can be divided into three geographical groups: the American group, Asiatic group, and European and middle-Asian group. Vitis vinifera L. is a predominant commercial species grown all over the world, is the only member in the European and middle-Asian group, and has given rise to thousands of cultivars. The American group accounts for about 30 species, and a similar figure was estimated for the Asiatic group. Three species (V. rotundifolia Michx., V. munsoniana Simpson ex Munson, and V. popenoei Fennell) have been identified in the subgenus Muscadinia, Vitis rotundifolia, normally referred to as the muscadine grape, is the only species within Muscadinia with commercial value; however, hybridization with the two other species has broadened the genetic base for breeding improved forms of the muscadine.
The muscadine grape (Vitis rotundifolia Michx.) is native to the southeastern United States and was the first native grape species to be cultivated in North America. Wild muscadine grapes are functionally dioecious due to incomplete stamen formation in female vines and incomplete pistil formation in male vines. Male vines account for the majority of the wild muscadine grape population. Muscadine grapes are late in breaking bud in the spring and require 100-120 days to mature fruit. Typically, muscadine grapes in the wild bear dark fruit with usually 4 to 10 fruit per cluster. Bronze-fruited muscadine grapes (albino mutants) were likely found in the wild, propagated and grown in gardens as early as the early 1700's (Lawson, J. 1714. History of Carolina. W. Taylor and J. Baker, London). These eventually formed the basis of a fledgling wine industry, and in 1811, the name Scuppernong, a corruption of the native Algonquin Indian name for the locale of this industry, was applied to these bronze grapes. (Reimer, F. C. 1909. Scuppernong and other muscadine grapes: origin and importance. N. C. Agr. Expt. Sta. Bul. 201.) Bronze-fruited vines, probably mixtures of seedlings or genetic variants under the generic name Scuppernong formed the basis of a thriving wine industry from the late 1800's until Prohibition (Gohdes, C. 1982. Scuppernong, North Carolina's grape and its wines. Duke Univ., Durham, N.C.). Five distinct strains of grapes under the name Scuppernong have been identified (Woodroof, J. G. 1934. Five Strains of the Scuppernong Variety of Muscadine Grapes. Proc. Am. Soc. Hort. Sci. 32:384-385). There are over 100 improved cultivars of muscadine grapes that vary in size from ¼ to ½ inches in diameter and 4 to 15 grams in weight. Skin color ranges from light bronze to pink to purple to black. The flesh is clear and translucent for all muscadine grape berries with thick, tough skin and mucilaginous flesh; however, breeding efforts within Muscadinia have developed forms with superior textural qualities such as tender, crunchy skin and meaty/melting flesh. Muscadine berries are popular for making into wine, pies and jellies.
The morphological traits that further distinguish Muscadinia from Euvitis are that Muscadinia has unbranched tendrils, pith continuous through the node, conspicuous lenticels on the developing bark of current year shoots, and wood with a specific gravity greater than 1, meaning that it sinks in water.
Vitis rotundifolia is characterized by remarkable overall health, including high disease, insect, and nematode resistance. Muscadines have resistance to most Euvitis fungal diseases and Pierce's disease (PD), caused by the bacterium Xylella fastidiosa Wells, a limiting factor in the production of V. vinifera grapes in the southeastern United States. Euvitis species native to the southeastern United States have resistance or tolerance to most of these pests, and bunch grape hybrids with V. vinifera have been bred and have positive traits such as large cluster, edible skin and pulp and seedlessness, which have not been found in muscadine grapes. However, none of these Euvitis hybrids possess the strength of resistance and overall health of the muscadine. Hybridization of bunch grapes and muscadines to combine bunch grape fruit quality with superior health of Muscadinia has been a long-term goal for grape breeders.
The absence of seedlessness is the major obstacle for wide acceptance of muscadine grapes in the fresh fruit market. In contrast, seedlessness due to stenospermocarpy (SSC) has been well known in bunch grapes. SSC in grapes is characterized by abortion of ovule/seed development post syngamy and is distinguished from parthenocarpy, which is defined as the development of a seedless berry in the absence of syngamy. Nearly all of the commercially important seedless grape cultivars worldwide (primarily of the Euvitis species Vitis vinifera L.) exhibit SSC because parthenocarpic berries are unacceptably small by comparison. SSC likely occurred as a mutation in V. vinifera in Eurasia that was selected and perpetuated via asexual propagation since hardwood cuttings are easily rooted. There are no reports of a similar mutation in the domesticated Muscadinia species V. rotundifolia Michx., despite having been cultivated commercially for several hundred years over thousands of acres in its native habitat in the southeastern U.S.
Intersubgeneric crosses between muscadine and bunch grapes have been performed for more than a century by breeders in several grape breeding programs. Vitis rotundifolia will hybridize readily with some species of Euvitis when used as the male parent, but will rarely hybridize when used as the female parent. The failure to produce hybrids from the muscadine stigma pollinated with bunch grape pollen in various attempts over a century clearly indicates that a unilateral incompatibility exists between the Muscadinia×Euvitis crosses.
Therefore, it is desirable to combine the seedless characteristic of bunch grapes with the superior characteristics of the muscadine grape to develop a seedless muscadine grape variety.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification.